The present invention is directed to a system and method for providing voice data services over an access network supporting a digital packet-based transport protocol, such as Digital Subscriber Line (DSL) technology. In addition, the present invention is directed to a system and method for providing conventional analog telephone service to supplement service provided through a digital-packet based transport network.
Conventional or xe2x80x9cplain old telephone signalxe2x80x9d (POTS) telephone service is provided over an xe2x80x9canalog loopxe2x80x9d that carries audio communications and signaling between a customer""s telephone device(s) and the telephone company""s wire center. A fundamental attraction of this technology is that power for the connection is provided from the wire center, and thus, with proper stand-by power systems at that location, telephone service remains available even when the customer""s power is interrupted. Additionally, only a simple, and generally very reliable, telephone set is required at the customer""s location, resulting in a service that is subject to minimal interruption.
Increasingly, telephone companies have used more sophisticated digital technology to deliver telephone service; this approach requires more complex equipment at the subscriber""s location and that equipment is, inherently, subject to additional failure modes and requires local powering. Typically, this equipment is installed at larger business locations where it may be practical to also install stand-by power equipment and redundant electronics, so that at least some telephone service can be maintained even when equipment or conventional power fails. The telecom industry is anxious to bring the advantages of digital technology to residential subscribers, preferably without giving up the reliability associated with conventional analog phone service. It is, generally, not cost-effective to equip the residential subscriber with stand-by power equipment and redundant electronics.
DSL is a high bandwidth technology that enables data to be transferred to and from individual subscriber locations at various speeds, currently ranging as high as 2 Mbps. Data is transferred over a DSL access portion of a local packet network (LPN) as xe2x80x9cpackets,xe2x80x9d and packets move over the LPN only when information is moving to or from the subscriber, and the line is in an idle condition otherwise. An LPN is a network that provides data connections among subscribers in a local service area with various connection types and data rates. Typically, an LPN consists of a plurality of DSL multiplexers and data switches. DSL equipment is designed to serve large numbers of subscribers, resulting in relatively low per-subscriber costs.
DSL technology is a very cost-effective mechanism for delivering high-bandwidth digital data to a residential subscriber. Some variants of DSL, in particular, Asymmetric Digital Subscriber Line (ADSL) permit the superposition of the high-bandwidth digital data stream on top of traditional analog telephone service. This is accomplished through the use of a readily available splitter/combiner device installed both at the wire center and at the subscriber""s premises. Voice communications can then be provided both by the analog signal, and by additional digital channels derived from the digital stream (as explained in above). However, as noted, providing the analog voice service requires POTS-compatible equipment in the WC. Typically, this equipment is large and expensive, and requires special connections, using time-division multiplexing, to the rest of the telephone network.
The aforementioned co-pending application provides a system and methods that enable facilities-based full service Competitive Local Exchange Carriers (CLECs) to transport local telephone service, including multiple voice call service, and data services to small and medium-sized business customers over an access network that supports a digital packet-based transport protocol, preferably over existing copper wire pair lines.
A telephone company deploying the technology above may want to offer the advantages of the analog POTS capability of ADSL, but cannot cost-justify the traditional switching technology required at the wire center. They need a mechanism that leverages their investment in packet-based technology but still delivers the benefits of traditional POTS, including continuous operation even when the customer""s power fails.
Briefly, the present invention is directed to a system and method for utilizing a local packet network (LPN) that supports a digital packet-based transport architecture, such as Digital Subscriber Line (DSL), to provide voice and optionally data services over a single local loop, such as a DSL, to a customer site. Multiple voice telephone calls as well as data services for a customer site are supported on a single DSL connected to that customer site.
At a customer site, a plurality of telephone devices (such as telephones, facsimile machines, modems and/or office telephone system ports) and data devices (such as those connected by a local area network) are interfaced to a local loop link connected to the LPN. Analog telephone signals (representing voice, facsimile signals, or modem signals) received from the plurality of telephone devices are converted to digital voice-band packets. Control signals representing off-hook, dial tone, call setup information, and other call control signals are converted to digital call control packets. The voice-band packets, call control packets and data packets (from the data devices at the customer site) are modulated for transmission via the local loop link over the LPN. In the reverse direction, modulated voice-band packets, data packets and call control packets received from the LPN destined for the customer site via the LPN on the local loop link are demodulated. The demodulated voice-band packets are converted to analog telephone signals for connection to appropriate ones of the plurality of telephone devices at the customer site. The demodulated data packets are coupled to the data devices (in the local area network) at the customer site. The demodulated call control packets are processed to control call setup and maintenance functions at the customer site.
At a control site within or connected to the LPN (such as a central switching facility), voice-band packets, call control packets and data packets from the customer site are received via the,LPN. The voice-band packets received from the customer site via the LPN are converted to time-division multiplexed signals and are coupled to a public switched telephone network (PSTN) switch in assigned time slots. Data packets received from the customer site are coupled to a data switch for transfer to a data network (such as the Internet). The call control packets are processed to control call setup and maintenance functions at the control site. In the reverse direction, data packets destined for the customer site are received from the data switch and coupled to the LPN for transmission to the customer site. Time-division multiplexed voice signals received from the PSTN switch destined for the customer site are converted to voice-band packets and are coupled to the LPN for transmission to the customer site.
A specialized apparatus called a remote digital terminal (RDT) is provided at the customer site and another specialized apparatus, called a host digital terminal (HDT) is provided at the central switching facility. Alternatively, the specialized functions of the HDT are integrated into a data switch in the LPN or into a PSTN switch. Similarly, the functions of the RDT can be integrated into a key telephone system/private branch exchange device or other equipment at the customer site. The RDT and HDT transport digitized voice-band packets and data packets between each other via the LPN. The RDT converts the voice-band packets suitable for communication over the LPN to and from analog telephone signals suitable for use by attached telephone devices. Similarly, the HDT converts voice-band packets to and from a time-division multiplexed format suitable for communication via the PSTN switch.
An apparatus called a wire center remote digital terminal (WC-RDT) is provided at a wire center to interface a plurality of local loop links with a digital subscriber line access multiplexer (DSLAM) in order to provide POTS service on the local loop links to customer sites. The WC-RDT is used to provide POTS service to customer sites having an RDT as well as to customer sites that do not have an RDT.